WO2011064261A1

WO2011064261A1 - Electrostructural stiffener made of a composite material

Info

Publication number: WO2011064261A1
Application number: PCT/EP2010/068141
Authority: WO
Inventors: Jesus Aspas Puertolas; Nicolas Maisonnave
Original assignee: European Aeronautic Defence And Space Company Eads France
Priority date: 2009-11-25
Filing date: 2010-11-24
Publication date: 2011-06-03
Also published as: FR2953092A1; FR2953092B1

Abstract

The invention relates to a structural stiffener made of a layered composite material comprising a head (11) held at a distance from a sole plate by means of which said stiffener is intended to be attached to a panel. The head (11) comprises an assembly of stacked layers, including at least one fiber-based structural layer (111), at least one layer having insulating properties (118) and at least one conductive network layer (113) inserted between said structural layer and said insulating layer, and comprising a network of electrical conductive elements (120), each of which originates at a first end close to a longitudinal end of the stiffener and terminates at an end opposite an opposing longitudinal end of the stiffener.

Description

ELECTRO-STRUCTURAL STIFFENER IN COMPOSITE MATERIAL

The present invention relates to a stiffener composite laminate material to be fixed on a panel to stiffen, including a panel used for the manufacture of working aeronautical structures, and an assembly of panels each comprising at least one stiffener according to the invention.

The invention is more particularly in the field of the installation of an electrical network in an aircraft.

The use of composite materials is nowadays widespread in many industrial fields, especially in the fields of aeronautics and aerospace. Thus, the working structures of aircraft are generally made based panels of composite materials with fibrous reinforcement, constituting for example fuselage sections. The combined properties of lightness and mechanical strength of such panels make it possible to manufacture working structures that are lighter than using conventional materials, but of equivalent mechanical strength, and thus to manufacture an aircraft that consumes less energy and is capable of to carry a larger payload.

The manufacture of working structures requires a step of structural dimensioning of the panels in which the stresses to which the different structures will be subjected (mechanical, thermal, etc.) are identified, and the characteristics of the composites composing them are determined.

After the manufacture of the working structures, the various systems that comprise the aircraft are installed. An aircraft generally comprises several types of systems such as electrical / electronic systems, such as avionics, the power distribution network, or the passenger data transmission network, such as the audio / video signals of the entertainment system. . The installation of electric and electronic systems, which are more and more numerous and complex, requires deploying a plurality of cable bundles which are generally held by supports fixed on working structures. These bundles of cables are exposed to possible sources of damage.

The present invention aims to propose a solution to ensure the deployment of an electrical network in the working structures of aircraft formed panel assemblies, which allows both to obtain a gain in mass of the structure equipped in its entirety and to protect the electrical network both during assembly operations of the panels to each other than during the subsequent use of the structure. The invention also aims that the installation operations of electrical / electronic systems in the structure are simple and quick to implement.

At the origin of the invention, the present inventors had the idea of taking advantage of the stiffeners which are used in a conventional manner to reinforce the panels used in the constitution of aircraft structures, and in particular fuselages. These stiffeners are generally formed of laminated composite material and they are fixed on the surface of the panels so as to extend longitudinally over the entire length of the latter.

According to the invention, the electrical conductor elements forming part of the electrical / electronic systems to be deployed in the structure are advantageously integrated in the thickness of the stiffener, in the form of an intra-laminar layer, and moreover in a part stiffener which is not involved for fixing to the panel to stiffen. When assembling the panels, it is sufficient to electrically connect these conductive elements from one stiffener to the other to obtain, without risk of damaging the conductive elements, an electrical system deploying in the structure thus formed by the assembled panels .

Thus, a structural stiffener laminated composite material according to the invention, comprising a head held at a distance from a soleplate by which the stiffener is intended to be fixed to a panel, is characterized in that said head comprises a set of superimposed layers, including at least one fiber-based structural layer, at least one layer with insulating properties and at least one conductive layer said interposed network between the structural layer and the insulating layer, comprising an array of electrical conductive elements each originating at a first end near a longitudinal end of the stiffener and terminating at an end opposite to an opposite longitudinal end of the stiffener.

The structural layer is preferably made of carbon fibers in a matrix resin. The insulating layer is preferably also a fiber-based structural layer, the latter being chosen to have electrical insulation properties, such as glass or aramid fibers. Thus, the conductive elements are advantageously protected between two layers having a high mechanical rigidity which surround them.

In order to mechanically balance the stiffener structure, the layers with insulating properties and the at least one intercalated conductive layer are sandwiched between two structural layers.

The stiffener according to the invention is conventionally in the form of an elongate piece, that is to say having a length, measured along the longitudinal direction, much greater than a width measured in a transverse direction. It comprises a head and at least one sole, connected to each other by at least one core, or the sole (s) for fixing the stiffener to the panel by any means, including screwing, gluing or riveting. This stiffener can have any shape known in itself for this type of parts and meeting the above characteristics, especially a so-called J, C or Z shape. In preferred embodiments of the invention, the stiffener has a shaped section called omega, or Ω. It comprises a head which is connected by two souls respectively to two soles. Such a stiffener has particularly advantageous structural characteristics. According to the invention, the stiffener head is formed of superimposed layers in the direction of its thickness, and preferably comprising at least one layer at a lower face of the head opposite the soleplate. structural fiber-based structure held in a matrix. Such a structural layer may in particular be formed from a stack of folds.

Fixing the stiffeners to the structural panels being effected by means of their sole (s), it is advantageously not risk during fixing operations to damage the electrical conductive elements that are integrated in the head. In addition, the assembly of a panel to another not necessarily involving fixing at the stiffener, or, if it is the case, such a fixing can advantageously be achieved only by the sole of the stiffener, remotely of the head incorporating the electrical conductor elements, the latter are thus protected during assembly operations of respective panels to each other.

According to an advantageous characteristic of the invention, the stiffener head comprises a plurality of network conductive layers, and at least one electrically conductive continuous layer, preferably substantially the width and length of the head, sandwiched between two conductive layers. successive networks. The continuous conductive layer advantageously forms an electrical shielding between the two network conductive layers. It may also, in preferred embodiments of the invention, provide an electrical reference for the installation of electrical / electronic systems. It is preferably made of a metal sheet. The invention does not, however, exclude any other embodiment known per se, such as for example a layer of a cellular metal material, a mesh or a metal foam.

Preferably, in the embodiments in which the stiffener head has a plurality of network layers, the conductive elements of successive layers are offset relative to each other, so that the electromagnetic interferences between a layer and another are advantageously further reduced.

In preferred embodiments of the invention, each layer having electrically conductive properties of the head, whether it be a network conducting layer as defined above or a continuous layer, is arranged between two layers with electrically insulating properties. In general, the insulating layers are preferably structural layers based on electrically insulating fibers held in an electrically insulating resin. The fibers are electrically insulating and may be both inorganic, such as glass fibers, and organic, such as aramid fibers.

Preferably, the stiffener head according to the invention comprises at least one structural layer based on carbon fibers, and a layer with electrically insulating properties which is interposed between each structural layer based on carbon fibers and each network conducting layer. adjacent.

In general, the number, the nature and the thickness of the structural layers are determined, according to calculations within the abilities of those skilled in the art, so as to give the stiffener the structural properties required to obtain adequate stiffening of the panel, by taking into account the fact that the network layers, the continuous layers and the insulating layers advantageously contribute to the mechanical performance of the stiffener.

According to an advantageous characteristic of the invention, the stiffener preferably comprises at each of its opposite longitudinal ends electrical connection means to which electrically conductive elements of the at least one network conducting layer are electrically connected.

In embodiments of the invention, these electrical connection means are external connectors disposed on the surface of an interconnection face of said stiffener.

In other embodiments, which may be associated with the previous ones within the same stiffener, these electrical connection means are connectors integrated on the surface of an interconnection face of said stiffener.

In other embodiments, which may be associated with the previous ones within the same stiffener, these electrical connection means are metallized holes or metal inserts opening on an interconnection face of said stiffener.

Metallic hole means holes whose surface receives after drilling an electrically conductive coating, for example in the form of a conductive paint.

The invention also relates to an assembly of panels each stiffened by at least one stiffener according to the invention, which is fixed on its surface by its sole.

The head of a stiffener of a first panel is electrically connected to the head of a stiffener of a second panel by electrical interconnection means, such as electrical cables, connecting electrical conductor elements of the stiffener head from the first panel to electrically conductive elements of the stiffener head of the second panel.

In preferred embodiments of the invention, the electrical interconnection means are carried by a splint, preferably of shape complementary to the shape of said stiffeners, ensuring a mechanical attachment between said stiffeners. Advantageously, a so-called strong coupling is obtained between the stiffeners, the splice advantageously producing both the electrical connection and a mechanical connection between the ends of the stiffeners arranged facing each other and substantially in alignment with one another. 'other.

The invention also relates to an assembly comprising two stiffeners according to the invention and a mechanical connection splice said stiffeners, of shape complementary to the shape of these stiffeners, and carrying electrical interconnection means able to interact in the position of mechanical connection with conductive elements of each of the stiffeners so as to transmit the electrical signals from one stiffener to the other.

The final working structure obtained by assembling panels stiffened by stiffeners according to the present invention then advantageously comprises an integrated electrical network. The electrical signals of this network are advantageously transported by the stiffeners which at the same time realize, in a conventional manner, the stiffening of the panels.

This structure has a saving in mass and a small footprint compared to the structures of the prior art equipped with a conventional electrical network. The installation operations of the electrical network within this structure are simple to implement, since it is sufficient to electrically interconnect the stiffeners fixed on the panels to each other. The electromagnetic compatibility of the structure is improved compared to the solutions of the prior art. The electrical conductive elements are furthermore advantageously protected in the thickness of the head of the stiffeners, by means of isolation and segregation. It follows from all these advantageous features a reduction in the manufacturing costs of the structures thus formed compared to the solutions of the prior art.

A detailed description of preferred embodiments of the invention is given below, by way of illustration only, with reference to FIGS. 1 to 8 which represent:

Figure 1 is a perspective view of a stiffened panel by means of a structural stiffener according to the invention;

Figure 2 is an exploded schematic view of a head of a stiffener according to the invention formed of superposed layers;

Figure 3 is a sectional view along a longitudinal plane of a longitudinal end of the head of a stiffener according to the invention;

Figure 4 is a top view of a longitudinal end of the head of Figure 3;

FIG. 5, an exemplary embodiment of electrical interconnection means of two stiffeners, Figure 6 is a perspective view illustrating the assembly of two stiffeners to one another by means of a splint;

Figure 7 is a schematic perspective view of the heads of the two stiffeners and the splint illustrating the electrical assembly of the two stiffeners by the splint of Figure 6;

Figure 8, a section along the plane A-A elements of Figure 7.

An example of a stiffener 1 according to the invention is shown in FIG. This stiffener has a so-called omega section, having a head 1 1, connected by two webs 12 respectively to two flanges 13. The stiffener is fixed on one side of a panel 2, for example an aircraft fuselage panel , by the two flanges 13, by fastening means designated by the reference 21 in the figure, which are conventional in themselves.

The invention does not exclude that the stiffener 1 has any other form known to those skilled in the art, for example a J-shaped section, C or W, since such a shape comprises a head separate from a sole used for attachment to the support panel.

The stiffener 1 has an elongate shape. It is fixed, conventionally, longitudinally on the panel 2, so as to occupy substantially the entire length, the longitudinal ends 14, 15 of the head 1 1 coming substantially at respective opposite longitudinal edges 22, 23 of the panel.

The head 1 1 has a lower face 16 disposed on the side of the flanges 13, and an opposite upper face 17.

The stiffener 1 is formed of laminated composite material. Its head 1 1 comprises a set of superimposed layers in the direction of its thickness, including at least one fiber-based structural layer in a matrix, an insulating layer and a so-called network layer comprising an array of electrically conductive elements, interposed between the layer structural and the insulating layer.

An embodiment of this head is shown in FIG.

Preferably, the various layers that compose it are all substantially of the same shape and the same surface dimension.

The head 1 1 comprises, at its lower face 16, a composite structural layer 1 1 1, called base, and at its upper face 17, a composite base structural layer 1 19. Preferably, the two layers 11 1, 1 19 comprise a fold or a stack of plies formed of fibers impregnated with a matrix resin. The fibers may be oriented unidirectionally and / or woven or braided. It is preferably carbon fibers, which in particular have the advantage of good mechanical strength combined with great lightness. The resin used to form this layer may be of any type, both thermosetting and thermoplastic.

The head 1 1 also comprises at least one network conductive layer 1 13. In the embodiment shown in the figure, it comprises for example two network layers 1 13, 1 17, which are preferably of the same kind.

The network layers 1 13, 1 17 comprise an array of electrically conductive elements 120, for example electrical cables, which are not in contact with one another and which are preferably arranged substantially evenly throughout the head stiffener 1 1. For example, the conductive elements 120 are substantially parallel to each other and spaced at a substantially regular pitch throughout the width of the head.

The conductive elements 120 are preferably formed of a material having a good conductivity / density ratio, such as aluminum. They preferably, but not necessarily, have substantially the same section. The section is in particular determined, by calculations within the reach of the person skilled in the art, according to the characteristics of the electrical signals to be pass. The spacing between the elements is preferably such that interference between two neighboring elements is minimized.

These conductive elements 120 may be included in a layer of dielectric material providing the structural connection with the layers that surround them. This dielectric material is for example a thermosetting resin, such as an epoxy resin, or a thermoplastic resin, preferably of the same composition as the resin forming the matrix of the basic structural layers 1 1 1, 1 19.

In a particular embodiment, the conductive elements are arranged in the manner of a printed circuit, for transmitting the electrical signals in different directions, while preferably distributed substantially uniformly throughout the head 1 January.

In embodiments in which the head 1 1 integrates several network conductive layers 1 13, 1 17, the conductive elements of the adjacent layers are preferably offset relative to each other, so as to minimize the electromagnetic interference between the two layers.

Each conductive element 120 has two ends and is arranged in the head 1 1 so that each of these ends is located respectively close to a longitudinal end 14, 15 of the stiffener head.

Between two successive network conductor layers 1 13, 1 17, a continuous conductive layer 1 15 is provided, preferably but not exclusively in the form of a metal foil, for example aluminum or copper. This continuous layer advantageously provides electrical shielding between the network layers 1 13, 1 17. Due to its metallic and continuous nature, it also participates substantially homogeneously to the mechanical characteristics of the head 1 January. It is furthermore capable of providing an electrical reference, for example a reference common to all the electrical signals transmitted by the network layers 1 13, 1 17, such as the electrical ground. Between the basic structural layer 1 1 1 and the first adjacent network layer 1 13, at least one layer with electrically insulating properties is interposed, preferably a structural layer 1 12 based on fibers with electrically insulating properties, called an insulating layer. Preferably, the insulating layer 1 12 comprises a fold or a stack of folds formed of fibers with electrically insulating properties impregnated with an electrically insulating matrix resin. These fibers may be of any type, for example glass or aramid. The matrix resin in this layer is preferably the same as that forming the basic structural layer 1 1 1.

An insulating layer, preferably of the same kind, is likewise arranged between each network layer and each continuous conductive layer.

Thus, an insulating layer 1 14 is disposed between the network layer 1 13 and the continuous conductive layer 1 15, and an insulating layer 1 16 is disposed between the latter and the network layer 1 17.

Finally, an insulating layer 1 18 is disposed between the network layer 1 17 and the basic structural layer 1 19.

All these insulating layers 1 14, 1 16, 1 18 are, just like the first insulating layer 1 12, preferably structural layers based on glass fibers or aramid.

In general, the head 1 1 of the stiffener according to the invention thus consists of successive layers superimposed on each other. In particular, it comprises a plurality of network conducting layers and continuous conducting layers interposed between two successive network layers, so as to reduce the electromagnetic interference between one and the other. A layer, preferably structural, with electrically insulating properties is interposed between the layers of a pair of successive electrically conductive layers, whether it is a network layer, a continuous layer or a structural layer based on carbon fibers. The head 1 1 may for example be formed by a conventional method such as the resin transfer method, said RTM process, in which is made by draping different folds on each other a dry preform, characteristics and a shape adapted to that of the composite material part to achieve, then infused into the set of plies so deposited a resin that can be thermoplastic or thermosetting, and it causes the curing of the resin.

According to the invention, the preform consists of a superposition, for the structural layers, of sheets or fabrics of fibers, dried or pre-impregnated with resin, and for the conductive layers, of metal sheets and element networks. electrically conductive.

The plies are preferably formed from carbon fibers for the basic structural layer 1 1 1, and glass or aramid for the structural insulating layers 1 12, 1 14, 1 16, 1 18. The number and the The nature of the pleats is determined so as to provide the desired final mechanical properties for the stiffener.

The different plies are deposited successively on a shape or a mold whose shape and volume substantially correspond to the shape and dimensions of the part to be produced, to produce the preform.

In a second step, the preform is impregnated with a resin, for example thermosetting, according to the RTM method. The resin is injected so as to spread uniformly in the internal space defined by the mold, by filling the void zones between the constituents of the different layers.

Finally, the resin is hardened so as to secure the different plies. At the end of this step, the part is removed from the mold and subjected, if necessary, to finishing operations, for example drilling or machining according to its intended use.

In the stiffener head thus obtained, the conductive elements 120 play a particular structural role and they contribute to the mechanical strength of the part.

Souls and soles are made, for example, so conventional, by a stack of plies formed of fibers impregnated with a matrix resin.

The structural head 11, due to the presence of the conductive elements 120 integrated in its thickness, is able to transmit electrical signals from one end to the other of each conductive element, such as data or control signals, and / or conduct electric currents in the case of a power supply.

At each longitudinal end 14, 15 of the head 1 1, at least a portion of the conductive elements 120 are connected to electrical connection means.

These connection means may be of several forms, two different embodiments of which are illustrated in FIG.

According to a first embodiment, the electrical connection means are internal connectors, in this case metallized holes 121, which open on an interconnection face of the head constituted by the upper face 17 of the latter in the embodiment shown in the figure, in the vicinity of a longitudinal end 14 of the head 1 January. Each hole 121 is further electrically connected to an electrical element 120 of the network layer.

According to another embodiment, the electrical connection means are constituted by a recess of the upper layers 1 14, 1 15, 1 16, 1 17, 1 18 so as to flush the conductive elements 120 exposed on one side of interconnection of the head 1 1, which in this case is constituted locally by an upper face 122 of the network layer 1 13.

These two embodiments can be implemented jointly for the same head January 1, which then has at a longitudinal end 14 two different interconnection faces, one of which is constituted by the upper face 17 of the head, and other by the upper face of the network layer 1 13 itself, as illustrated in Figures 3 and 4.

According to other embodiments which have not been shown in the figures, the electrical connection means can be connectors external surfaces mounted on the surface of the head 1 1 on an interconnection face, for example in the form of a flat multi-pin connector, each pin being connected to a conductive element 120, or integrated internal connectors between layers forming the head, for a connection via an interconnection face, which may for example be a slice of the head.

The electrical connection means are not limited to the means described, and all the conventional connectors used for the electrical / electronic connection, external or internal, can also be used in the context of the invention.

The connecting means associated with different stiffeners can be electrically connected to each other via interconnection means, such as coaxial cables, a computer web or any type of electrical cable capable of conveying one or more electrical signals.

The interconnection means between two heads 1 1, 1 1 'of two stiffeners 1, 1' belonging to different panels 2, 2 'may in particular be constituted by conventional cables 130 in themselves, as illustrated in FIG. 5 In this case, a coupling is obtained between the two stiffeners 1, 1 'which is said to be weak, that is to say only electrical.

In the case of connection means constituted by metallized holes 121, conductive elements 120 of a first stiffener 1 are for example connected to elements 120 'of a second stiffener 1' by interconnection means such as jumpers in U, which are not represented in the figures and which are conventional in themselves.

In other embodiments of the connection between two stiffeners 1, 1 ', as illustrated in FIGS. 6 to 8, a splice 3 is used which advantageously has a shape substantially identical to that of the stiffeners, that is to say i.e., in the preferred embodiment shown in the figures, an omega-shaped section splice. Such a joint, known in itself, avoids the need to install fasteners in the core and the head stiffeners, limiting itself to a fixation at the level of the soles, while ensuring the continuity of the transmission of longitudinal forces a stiffener to the other.

In a conventional manner, such a splint comprises a head 31, two webs 32 and two flanges 33 by which the splice 3 can be fixed respectively to the flanges 13, 13 'of the stiffeners 1, Y. The internal dimensions of the splice 3 are in particular determined to allow to overlap partially simultaneously to each of the stiffeners, ensuring the contact of the soles of the splint with the soles of the stiffeners.

Under a lower face, the head 31 of the splint comprises electrical interconnection means 34, which may be of any type, for example electrical cables, and which are preferably fixed under a lower protuberance 35 which the head of the splice comprises. the splice. When the splice 3 is fixed to the stiffeners 1, Y so as to ensure the mechanical connection, these interconnection means 34 are able to interact with the connection means carried by the head 1 1, 1 1 'of each of the stiffeners for example, in the preferred embodiment shown in the figures, with the electrical conducting elements 120, 120 'flush with the surface of the interconnection faces 122, 122' of the heads 1 1, 1 1 '. They thus provide the electrical interconnection between conductive elements 120 of a first stiffener 1 and conductive elements 120 'of a second stiffener Y. Means 36 for clamping the head 31 of the splice against the interconnection faces 122, 122 'respectively of the stiffener heads 1 1, 1 1', are further provided so as to ensure a close contact between the conductive elements 120, 120 ', or electrical connection means associated therewith, and the means In such an advantageous embodiment of the invention, the connection between two stiffeners 1, 1 'is made both mechanically and electrically by the same splint 3, which one part is fixed mechanically by its soles 33 to the flanges 13, 13 'of the stiffeners, and on the other hand at the same time provides an electrical connection between conductive elements of a stiffener and conductive elements of the other. A single operation of fixing the splice to the stiffeners advantageously makes it possible to achieve the mechanical and electrical connection between these stiffeners.

Continuous conducting layers, in cases where they constitute a reference layer of the electrical system, can also be electrically connected, in a similar manner, from one stiffener to another.

Conducting elements of different network layers of the same head can be electrically connected to each other, for example by means of a through connection.

The final structure, obtained by an assembly according to the invention, panels stiffened by stiffeners according to the invention advantageously comprises an integrated electrical / electronic system, which is protected from the risk of damage and which has been quite simple to set up in the structure.

Claims

1 - Structural stiffener (1) made of stratified composite material, comprising a head (1 1) held at a distance from a sole (13) by which said stiffener is intended to be fixed to a panel (2), characterized in that said head (1 1) comprises a set of superimposed layers including:

at least one fiber-based structural layer (1 1 1),

at least one layer with insulating properties (1 18),

and at least one network conducting layer (1 13) interposed between said structural layer and said insulating layer, comprising an array of electrical conducting elements (120) each originating at a first end near a longitudinal end (14). ) of said stiffener and terminating at an end opposite to an opposite longitudinal end (15) of said stiffener.

2-stiffener according to claim 1, characterized in that said head (1 1) comprises a plurality of network conductive layers (1 13, 1 17), and at least one continuous electrically conductive layer (1 15) interposed between two layers successive network conductors (1 13, 1 17).

3-stiffener according to claim 2, characterized in that the conductive elements (120) of successive network conductive layers (1 13, 1 17) are offset relative to each other. 4. Stiffener according to any one of claims 1 to 3, characterized in that each layer with electrically conductive properties (1 13, 1 15, 1 17) of said head (1 1) is disposed between two layers with electrically insulating properties (1 12, 1 14, 1 16, 1 18).

5. The stiffener as claimed in claim 1, wherein said head comprises at least one structural layer based on 1 12) interposed between each structural layer made of fibers of carbon and each adjacent network conductive layer.

6. Stiffener according to any one of claims 1 to 5, characterized in that at least one layer with insulating properties (1 18) is a structural layer based on electrically insulating fibers. 7- Stiffener according to any one of claims 1 to 6, characterized in that it comprises at each of said opposite longitudinal ends (14, 15) of the electrical connection means to which are connected electrically conductive elements (120) of the at least one network conductive layer (1 13, 1 17). 8- Stiffener according to claim 7, characterized in that said electrical connection means are connectors disposed on the surface of an interconnection face (122) of said stiffener (1).

9. Stiffener according to claim 7 or 8, characterized in that said electrical connection means are metallized holes (121) opening on an interconnection face (17) of said stiffener (1).

10- Stiffener according to any one of claims 1 to 9, characterized in that it has an omega-shaped section.

1 1 - Assembly of panels (2, 2 ') each stiffened by at least one stiffener (1, 1') according to any one of claims 1 to 10, which is fixed on its surface by said sole (13, 13 ') ), characterized in that the head (1 1) of a stiffener (1) of a first panel (2) is electrically connected to the head (1 1 ') of a stiffener (1') of a second panel (2 ') by electrical interconnection means (130, 34) connecting electrical conductor elements (120) of the head (1 1) of said stiffener of the first panel to electrical conductor elements (120') of the head ( 1 1 ') of said stiffener of the second panel.

12- Assembly according to claim 1 1, characterized in that the means electrical interconnection (34) are carried by a splice (3) providing a mechanical attachment between said stiffeners (1, 1 ').